Apparatus for catalytic conversion

ABSTRACT

A catalytic reactor in which feed, catalyst and diluent gas enter the bottom of a reactor which has a cross-sectional area which does not decrease substantially, preferably which has a substantially constant cross-sectional area, from the point at which catalyst and feed first come in contact to the reactor outlet. Atop the reactor is a disengagement vessel of relatively large diameter in which the product gases are separated from the catalyst. The catalyst drops through a stripper culminating in a bend which collects catalyst to provide a seal between the reactor and a regenerator. A lift line carries the catalyst to the top of the regenerator through which the catalyst moves downward to a transfer line that returns the catalyst to the reactor. Flue gases are removed from the top of the regenerator. The transfer line culminates in a bend to collect solid catalyst, providing a seal between the regenerator and the reactor. Fluidizing gas is introduced into the transfer line by an inlet probe which can be moved vertically so that the level within the transfer line at which the gas is introduced can be varied to control the catalyst flow rate. 
     An improved process of catalytic hydrocarbon conversion has also been discovered.

The present invention relates to an improved catalytic chemicalconversion unit. More particularly, the present invention relates to animproved apparatus and method for simulating progressive flow, e.g.,riser, chemical reaction, e.g., catalytic hydrocarbon cracking, on arelatively small scale, e.g., laboratory.

In many instances in the chemical process industries, chemical reactionstake place by contacting a catalyst, e.g., in the fluidized state, withreactants in a reaction system under substantially progressive flowconditions. For example, in the petroleum refining industry, catalytichydrocarbon cracking of higher boiling components to lower boilingmaterials often takes place in the presence of fluidized crackingcatalyst under substantially progressive flow conditions. Due to theconfiguration of many operational catalytic reaction systems, suchreaction under substantially progressive flow conditions is generallytermed "riser" reaction, e.g., "riser" cracking.

One problem which exists relative to such riser operations is the needto simulate this type of reaction on a small scale to test variousfeatures, e.g., process variables different catalysts and the like. Thissmall scale testing is desirable prior to incorporating such features ina commercially sized reaction system. However, commercial operation ofriser reaction systems has been found difficult to simulate on a smallscale. This is especially true when the commercial reaction system alsoinvolves continuous regeneration of the catalyst, such as is often thecase in catalytic hydrocarbon cracking. Thus, in small reactors in whichthe catalyst is passed through the reactor and transferred from thereactor to the regenerator and returned to the reactor in a cyclicmanner, the regulation of the small catalyst flow rate is very difficultand leads to inadequate control of the process, especially if the flowis regulated by a valve. The relatively small pressure drops existing insuch units is a significant factor making such control difficult. As anexamle, the differential pressure may not exceed about 1.5 psi.

Therefore, an object of the present invention is to provide a smallscale, e.g., laboratory, apparatus which gives improved simulation ofprogressive flow or riser chemical reaction, e.g., catalytic hydrocarboncracking.

Another object of the present invention is to provide an improvedchemical reaction process which allows improved simulation ofprogressive flow or riser chemical reaction, e.g., catalytic hydrocarboncracking operations. Other objects and advantages of the presentinvention will become apparent hereinafter.

The present invention involves improvement in the chemical conversionunit and process of U.S. Pat. No. 3,502,574. While this patented unitand process give beneficial results, it has been found that the presentchemical conversion unit and chemical conversion process provide evenmore improved simulation of progressive flow or riser chemical reactionoperations to permit more accurate evaluation of, for example, catalystsand process variables.

The present invention is a catalytic reactor which can be small in sizeand flexible in operation and yet which provides improved simulation ofriser reactor operation to permit accurate evaluation of catalysts andchemical processes.

The present chemical conversion unit can be small in size and flexiblein operation. This unit comprises a reactor column which discharges intoa disengagement vessel. Feed and finely divided catalyst enter in thebottom portion of the reactor column and are transported as apredominately lean fluid up to the disengagement vessel from whichproduct gases are drawn. As an essential characteristic of the presentinvention, the cross-sectional area of the reactor column does notdecrease substantially, preferably is maintained substantially constant,from the point at which the feed and finely divided catalyst first comeinto contact to the reactor column outlet. Finely divided catalyst,e.g., fluid type catalyst, can be used. Such catalyst particles oftenhave particle sizes in diameters ranging from about 20 to 150 microns.The spent or used catalyst passes downward from the disengagement vesselin a stripper through which a stripping gas rises to remove at least aportion of hydrocarbon products which are carried over with thecatalyst. The catalyst is then gas lifted to a regenerator, e.g., in adispersed fluid state. A regenerating gas, e.g., oxygen-containing gas,is introduced in the bottom portion of the regenerator. Thisregeneration gas acts to remove, e.g., combust carbonaceous depositsfrom the solid catalyst particles which are formed during chemicalreaction in the reaction column. Combustion gases are exhausted from theregenerator and can be further sampled and evaluated, if desired. Thebottom portion of the regenerator is coupled to the bottom portion ofthe reactor column to return the catalyst to the reactor column. Thus,the catalyst flows cyclically between the reactor column and theregenerator. A moveable gas inlet extends into a regenerator catalyststandpipe. The height of the inlet within the regenerator standpipecontrols division of the catalyst between a fluidized state and acompact state which in turn accurately controls the catalyst flow rateinto the reactor column. The bottom of the stripper leads to a catalystliftline which in turn, leads to the regenerator. Likewise, the bottomof the regenerator standpipe leads to the reactor column. Compact statesor phases of solid catalyst accumulate in the lower portions of both thestripper and regenerator standpipe and provide gas seals. The stripperand regenerator standpipe and their portions leading to or connectedwith the lines passing to the regenerator and reactor column,respectively, can operate without valve control. The fluistatic pressurewhich develops across the accumulated compact solid phases in both thestripper and standpipe bottoms, and the frictional resistanceencountered also affect the catalyst flow rate.

The various components of the present chemical conversion unit can haveany suitable configuration. However, because of ease of the fabrication,it is preferred that the reactor column, disengagement vessel, stripperand regenerator be generally circular in cross-section. It is importantthat the cross-sectional area of the reactor column does notsubstantially decrease, preferably is maintained substantially constant,from the point at which reactant or feed and finely divided solidcatalyst particles first come in contact to the reactor column outlet.

The chemical conversion unit of the present invention may be fabricatedfrom any suitable material of construction. The material of constructionused is dependent upon the particular application involved. In manyinstances, metals and metal alloys such as iron, carbon steel orstainless steel, copper and the like may be used. Of course, theapparatus should be made of a material or combination of materials whichis substantially unaffected by the catalyst particles, reactants and theconditions, e.g., temperature and the like, at which the unit normallyis operated. In addition, such material or materials should have nodetrimental effect upon the catalyst particles or reactants beingprocessed.

Although the present chemical conversion unit and process are applicableto a wide variety of chemical reactions, such unit and process areparticularly useful in the catalytic cracking of higher boilinghydrocarbon components to lower boiling materials such as gasoline,hexane, hexene, pentane, pentene, butane, butylene, propane, propylene,ethane, ethylene, methane and the like. Typically, the feed is apetroleum or other hydrocarbon gas oil and may often be a mixture ofstraight-run and recycle gas oils. Cracking conditions are well knownand often include temperatures from about 850°F. to about 1100°F.,preferably from about 860°F. to about 1050°F. Other reaction conditionsusually include pressures of up to about 100 psig., catalyst to oilratios of from about 5 to 1 to about 25 to 1, and weight hourly spacevelocities of from about 3 to about 60. These cracking conditions may bevaried depending on the feedstock and catalyst being used and theproduct wanted. The cracking reaction is generally conducted in theessential absence of added free hydrogen.

As noted above, the catalytic cracking system usually includes acatalyst regeneration zone in which a portion of the catalyst iswithdrawn from the cracking reactor and periodically contacted with freeoxygen-containing gas in order to restore or maintain the activity ofthe catalyst by removing, i.e., combusting, carbonaceous materialdeposited on the catalyst. The combustion gas temperature in theregeneration zone is generally from about 800°F. to about 1500°F.,preferably from about 900°F. to about 1300°F., and more preferably fromabout 1150°F. to about 1250°f. The regenerated catalyst is returned tothe cracking reactor.

Any hydrocarbon cracking catalyst having the requisite finely dividedsize, e.g., particles having an average diameter from about 20 micronsto about 150 microns, can be processed in the present chemicalconversion unit. For example, various conventional and well knownhydrocarbon cracking catalysts in the fluidized form can be soprocessed. Typical among these conventional compositions are those whichcomprise alumina, silica, silica-alumina, at least one crystallinealumino silicate having pore diameters of from about 8A to about 15A andmixtures thereof. At least a portion of the alumina, silica,silica-alumina and crystalline alumino-silicate may be replaced by clayswhich are conventionally used in cracking catalyst compositions. Typicalexamples of these clays include halloysite or dehydrated halloysite(kaolinite), montmorillonite, bentonite and mixtures thereof. Thesecatalyst compositions may also contain minor amounts of other inorganicoxides such as magnesia, zirconia, etc. When the catalyst containscrystalline alumino-silicate, the compositions may also include minoramounts of conventional metal promoters such as the rare earth metals,in particular, cerium.

The various gases employed in conjunction with the present invention,e.g., diluent gas, stripping and second stripping gas and lift gas andthe like, other than the oxygen-containing regeneration gas, may becomposed of various relatively inert gases, e.g., steam, helium neon,argon, nitrogen, mixtures thereof and the like. Because of availabilityand convenience, it is preferred that each of these gases be the same,more preferably, nitrogen. The oxygen-containing regeneration gas shouldinclude sufficient oxygen so as to combust the carbonaceous depositsfrom the catalyst in the regenerator. Because of availability andconvenience, the preferred oxygen-containing regeneration gas is air.

These and other aspects and advantages of the present invention will beapparent from the following detailed description and claims,particularly when read in conjunction with the accompanying drawingwhich is a side elevational view, partially in section, of a laboratoryfluid catalytic hydrocarbon cracking unit in accordance with the presentinvention.

As depicted in the drawing, the reactor column of the catalytic crackingunit is designated generally by reference numeral 8 and comprises acolumn having substantially a single diameter and, therefore, asubstantially single cross-sectional area. In the representative exampleof the drawing, reactor column 8 is made up of a stainless steel tubingand involves a series of vertical rises and falls connected by smoothu-bends.

A hydrocarbon feed to be cracked to lower boiling components, e.g., amineral gas oil which will be cracked to useful products such asgasoline, is introduced to the bottom of reactor column 8 at inlet 18,and a diluent gas, such as nitrogen, is introduced at inlet 20 to passthrough the reactor with the feed and catalyst. The feed and diluent gasmay be pre-heated before entering inlets 18 and 20 if desired.Circulating catalyst, e.g., any finely divided hydrocarbon crackingcatalyst, from smooth bend 43 enters the bottom portion of reactorcolumn 8. The catalyst and hydrocarbon are present in reactor column 8in a predominantly lean fluidized state. Such a predominantly leanfluidized state differs from a dense fluidized state or phase in thatsuch lean state involves substantially less catalyst per unit volumethan does the dense phase. The diameter of reactor column 8 remainssubstantially constant from inlet 18, the point at which feed from inlet18 first comes into contact with catalyst, to the reactor outlet atdisengagement vessel 22. Disengagement vessel 22 is mounted at the otherend of reactor column 8 and since the cross-secton of the disengagementvessel 22 is larger than that of reactor column 8, the disengagementvessel 22 permits expansion of the gaseous hydrocarbon products comingout of reactor column 8. These gaseous products pass through outlet pipe24 from the top of disengagement vessel 22 to product collectionapparatus, e.g., conventional gas collection means (not shown), topermit sampling and evaluation of the products.

The solid catalyst particles entering the disengagement vessel 22 fallinto stripper 26 which is a length of vertical pipe having a smooth bend27 at the bottom leading to catalyst lift line 30. Bend 27 causesaccumulation of a compact phase of solid catalyst particles at thebottom of stripper 26 below inlet line 28, without catching or holdingup any catalyst. Stripping gas, e.g., nitrogen, is introduced intostripper 26 at inlet 28 just above bend 27. The nitrogen removesproducts which may have been carried over into the stripper with thesolid catalyst particles. This stripping gas also emerges through outletpipe 24. The catalyst in stripper 26 which is above inlet 28 is in afluid phase or condition and the pressure exerted by the catalyst aboveinlet 28 is proportional to its depth. Thus, as the catalyst flow ratein reactor column 8 increases, the depth of catalyst in stripper 26above inlet 28 increases to raise the differential pressure betweenstripper 26 and catalyst lift line 30. The catalyst in the catalyst liftline 30 is in a relatively dispersed fluid state and exerts little, anda relatively constant, back pressure or resistance to flow.

The solid catalyst particles passing from the bottom of stripper 26enters vertical lift line 30. A lifting gas, such as, for example,nitrogen, is introduced into the bottom of lift line 30 at inlet 32.This gas lifts the solid catalyst through the small cross-section liftline to the top of regenerator vessel 34. The rate at which lifting gasis introduced into lift line 30 through inlet 32 is adjusted so that itsvelocity is great enough to lift the largest solid catalyst particlesutilized, maintaining a dilute phase in the lift line.

Solid catalyst particles which lie in bend 27 at the bottom of stripper26 are in a compact state and provide a gas seal between reactor column8 and regenerator 34. The fluistatic pressure across this compact phaseof solid catalyst particles controls the rate at which the solidcatalyst particles leave stripper 26 and enter lift line 30. The ratesof stripping and lifting gases introduced via inlets 28 and 32,respectively, are controlled so that the fluistatic pressure in liftline 30 is less than the pressure within stripper 26. This pressureimbalance results in the flow of solids from stripper 26 into lift line30. As operation stabilizes, the level of fluidized solid catalystparticles in the vertical section of stripper 26 builds up until therate of flow of catalyst out of the stripper 26 into lift line 30 isequal to the inlet rate of solid catalyst particles from disengagementvessel 22 to stripper 26.

Regenerator 34 comprises a vertical pipe 35 on the top of which islocated a large cross-section vessel 36 having, as shown, a 60° cone onits bottom and a 120° cone on its top. An oxygen-containing regeneratinggas, such as air which combusts or burns carbonaceous deposits from thecatalyst, is introduced into the bottom of regenerator 34 at inlet 38.This gas from inlet 38 and the gas entering moveable inlet 44 maintainthe solid catalyst particles within regenerator 34 in a fluidized stateduring which the catalyst is regenerated, for example, by removing,e.g., combusting, coke from it which has formed during the catalyticcracking of hydrocarbons in reactor column 8. The resulting combustionor flue gas passes through baffles 39 and 3a which are mounted withinvessel 36 to separate solids from the gas. Vessel 36 reduces thevelocity of the gas, allowing settling of the solid catalyst particles.The flue gas is carried away by outlet pipe 40, which emerges near thetop of vessel 36, above baffles 39 and 39a. Outlet pipe 40 carries theflue gas to other processing equipment (not shown) to permit samplingand evaluation, as desired.

Transfer line 42 couples the bottom of regenerator 34 to the bottom ofreactor column 8. The bottom of transfer line 42 incudes a smooth bend43 to enable connecton to the reactor. Bend 43 causes accumulation of acompact phase of solid catalyst at the bottom of transfer line 42,without catching any catalyst. Second stripping gas, such as nitrogen,is introduced into transfer line or standpipe 42 through moveable inlet44, which passes from the top of vessel 36 through regenerator 34 intotransfer line 42. This second stripping gas strips the air from thecatalyst, and the resulting gas leaves the system at outlet 40.

Within transfer line 42 and regenerator 34, dense fluidized catalystexists above the lower end of moveable inlet 44. Since moveable inlet 44can be moved vertically to adjust its depth within transfer line 42, thedepth of this fluidized phase can be controlled from the postion ofinlet 38 to the maximum insertion depth of moveable inlet 44. Belowmoveable inlet 44 a compact phase accumulates due to smooth bend 43 andforms a gas seal. As moveable inlet 44 is raised, the depth of thefluidized phase is decreased, and the depth of the more compact phase insmooth bend 43 is increased. Thus, as moveable inlet 44 is raised, thepressure differential between regenerator 34 and reactor column 8 isreduced and the frictional resistance to flow caused by the compactphase is increased.

Solid catalyst particle flow through the system is due to the pressuredifferentials across the compact catalyst phases which accumulate insmooth bends 27 and 43. When moveable inlet 44 is raised above inlet 38,the compact phase in smooth bend 43 is at its maximum size and theminimum pressure difference exists across the compact phase catalyst insmooth bend 43. This pressure differential is conveniently less thanthat required to cause catalyst flow. As moveable inlet 44 is loweredbelow inlet 38, the size of the compact phase decreases, the depth ofthe dense fluidized phase increases and as a result the pressuredifferential increases, and catalyst commences to flow from transferline 42 into reactor column 8.

Within stripper 26 the catalyst level also varies with the depth ofmoveable inlet 44. When moveable inlet 44 is lowered, the catalyst flowrate increases and as a result the catalyst level in stripper 26 risesand, thus, the pressure differential across the compact catalyst phasein smooth bend 27 increases. As a result, the catalyst flow rate throughstripper 26 increases to keep pace with the flow rate throughregenerator 34.

The substantially single cross-section of reactor column 8 results inimproved simulation of the operation of a riser reaction system. Thereactor column can have a small size usable, for example, in laboratoryoperations. For example, a reactor column 8 can have a total lengthranging from about 5 inches to about 30 feet, preferably from about 1foot to about 20 feet. The inside cross-sectonal area of reactor column8 can range from about 0.001 in.² to about 1 in.², preferaby from about0.01 in.² to about 0.50 in.².

The maximum height of the chemical conversion unit is determined by theheight of regenerator 34 and its vessel 36 which must permit thecatalyst in pipe 35 to be sufficiently above the outlet of reactorcolumn 8 to provide the required fluistatic pressure differentials.While the height of regenerator 34 is thus dependent upon the height ofreactor column 8, a regenarator height of about 15 feet above the bottomof reactor column 8 is a convenient maximum usable on a small scaleapparatus. In this type of equipment the diameter of the transfer line42 can range from about 0.5 inches to about 2 inches or more.

If desired, the temperature within the apparatus can be controlled atvarious points, for example, by means of electric heating coils andthermocouples (not shown) around or in reactor column 8, stripper 26,regenerator 34 and transfer line 42.

The following examples clearly illustrate the present invention.However, these examples are not to be interpreted as specificlimitations on the invention.

EXAMPLE 1 to 3

These examples illustrate the improved simulation of riser hydrocarboncracking operations provided by the present invention.

An apparatus similar to that depicted in the FIGURE was used inExample 1. Reactor column 8 was constructed of stainless steel tubing,was circular in cross-section and had an inside diameter of 0.245 inchesthroughout its length, from hydrocarbon feed inlet 18 to its outlet indisengaging vessel 22, of about 12.5 feet.

The apparatus employed in Example 2 was similar to that used in Example1 except that the first 21/4 inches of the reactor, i.e., the 21/4inches directly above the hydrocarbon feed inlet, had an inside diameterof 1/2 inch.

A third apparatus, used in Example 3, was similar to that used inExample 1 except that the reactor comprised a straight verticle taperedtube. This apparatus is similar in that disclosed and claimed in U.S.Pat. No. 3,502,574. The first or lowermost 21/4 inches of the reactorhas an inside diameter of 1/2 inch. This section is followed, inascending order, by four 71/4 inch lengths of pipes having insidediameters of 0.364 inch, 0.493 inch, 0.622 inch and 0.824 inch,respectively. The last or uppermost of these sections is truncated andterminates at the underside of the disengaging vessel.

Each of these apparatus was used to catalytically crack the followinghydrocabon feed:

    Gravity, °API                                                                              26.1                                                      Wt.% Sulfur         0.929                                                     Wt.% Nitrogen       0.108                                                     Wt.% Aromatics      40.1                                                      ASTM Distillation (D-1160)                                                      IBP (°F.)  472                                                         50%               776                                                         95%               1001                                                  

The catalyst employed in each run was a commercially used, crackingcatalyst in the form of fine particles having an average diameter ofabout 50 microns.

The tests were performed at the following conditions:

                    Ex. 1  Ex. 2    Ex. 3                                         Reaction Temperature, °F.                                                                928      930      933                                       Catalyst to Oil Wt. Ratio                                                                       9.6      7.8      7.9                                       Vol.% Conversion of Feed                                                                        73.2     73.2     71.5                                  

Selected results from these tests were as follows: ##EQU1##

Riser or progressive flow catalytic hydrocarbon cracking tends tominimize adverse secondary reactions, e.g., cracking of light olefins.See, for example, D. P. Bunn, Jr. et al, The Development and Operationof the Texaco Fluid Catalytic Cracking Process, American Institute ofChemical Engineers, Preprint 21A, Sixty-Fourth National Meeting, NewOrleans, Louisiana, Mar. 16-20, 1969. Thus, riser or progressive fowcatalytic cracking of hydrocarbons produces a higher proportion oflight, e.g., C₃ and C₄ olefins, relative to that produced, for example,in fluidized bed catalytic cracking. Therefore, it is clear that theapparatus of the present invention, Example 1, simulates riserhydrocarbon cracking operations more accurately than do the otherapparatus.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A catalytic chemicalconversion unit comprisinga. a reactor column having a lower inlet andan upper outlet; b. means for introducing a feed fluid into the lowerportion of said reactor; c. means for introducing finally divided solidcatalyst into the lower portion of said reactor, provided that thecross-sectional area of said reactor column is maintained substantiallyconstant from the first point at which said fluid and said catalyst arecontacted to said reactor column outlet; d. means for separatingchemical reaction products from catalyst passing from the reactoroutlet; e. a generally vertical catalyst stripper for collectingseparated catalyst; f. means for introducing a stripping gas into saidstripper to maintain an upper portion of the collected catalyst in adense fluidized state and a lower portion of the collected catalyst in acompact phase; g. catalyst lift means for conveying catalyst as adispersed phase between the lower portion of the stripper and a catalystregenerator; h. means for introducing a lifting gas into said catalystlift means; i. means for introducing a regenerating gas into saidregenerator to regenerate catalyst therein and maintain the catalyst ina dense fluidized state; j. transfer means for passing regeneratedcatalyst between said regenerator and said reactor inlet and includingmeans for causing catalyst to form a compact phase in the lower portionof said transfer means; and k. control means comprising a pipe passingthrough said catalyst regenerator to said transfer means and verticallymovable within said regenerator and said transfer means for introducinga fluidizing gas into said transfer means to vary the relative amountsof fluidized and compact catalyst in said transfer means to control therate of catalyst flow to said reactor.
 2. A unit as claimed in claim 1in which said control means is vertically movable at levels below saidregenerating gas introducing means to control catalyst flow.
 3. A unitas claimed in claim 2 in which said control means comprises a pipepassing through said catalyst regenerator to said transfer means andvertically movable within said regenerator and said transfer means.
 4. Aunit as claimed in claim 3 in which the cross-sectional area of saidreactor column is in the range from about 0.001 in.² to about 1 in.². 5.A unit as claimed in claim 2 in which the cross-sectional area of saidreactor column is in the range from about 0.001 in.² to about 1 in.².